1. Field of the Invention
The present invention relates to load lifting apparatus such as hooks and spreader beams normally used with cranes or other hoisting tackle or equipment, and more particularly, to load lifting apparatus having remote controlled load release capability.
2. Description of the Prior Art
Lifting devices and other apparatus used at the end of a lifting crane or other load bearing line are well developed in the prior art. Snap hooks, crane hooks, and other lifting apparatus are generally comprised of a hook shank which extends from the point of attachment of the hook to a load bearing line, down through an appropriate angle and a leading tip of the hook to form the shape to capture a chain, or other load bearing line secured to a load to be lifted by the hook, using a crane or other load bearing apparatus. The opening of a hook shape is sometimes referred to as the throat or mouth. There are a plethora of different hook designs which are employed in various applications, whether it be marine, industrial, or general categories of crane hooks for lifting loads or to affix the crane's load bearing line to a load to be lifted. The load or load bearing line is placed onto the hook through the throat of the hook.
A spreader beam is a generally linear lifting device having multiple, evenly-spaced load securing points. Spreader beams, or spreaders as they are commonly called, are frequently used to lift multiple identical items, such as metal or wood roof trusses. After a plurality of trusses are suspended from the spreader beam parallel to one another, the spreader beam and trusses are elevated with a crane and positioned on top of parallel, spaced-apart walls. After the trusses are secured to the walls, they are released from the spreader beam so that the latter can be reused. Typically, the lifted items are released from the spreader beam by a construction worker who climbs to the apex of each truss and releases each securing cable or chain individually. Depending on the height of the installed trusses, the release operation can be time consuming and pose the risk of a serious fall to the worker.
Although the use of spreader beams having hooks with open throats have been used on the sly to a limited extent, the use of such equipment is unsafe. While moving a load with a crane, occasionally the load may contact the ground or some other object and, thereby, become disengaged from the hook. The danger is exacerbated when a spreader beam is used, as the loss of an item suspended at one end of the beam will cause a serious imbalance problem with the remaining items, possibly causing unwanted release of all the suspended items.
The operator of the crane attached to the hook sometimes jogs the load to place the load in a specific targeted position before disengaging the hook from the load. Jogging is an operation to move a crane or trolley crane bridge in a series of short, discontinuous increments by momentary operation of a controller normally accomplished at the end of a lifting cycle to place a load in a precisely targeted resting point after conveyance of the load over a larger distance. Frequently, when jogging a hook or a spreader beam with multiple hooks, the suspended load will bounce off of the ground or other structures as it is finally moved into its desired position before release of the lifting apparatus. Premature or unintended release of loads or lifting straps affixed to loads occurs most frequently at this point in the operation of the apparatus, causing a hazardous condition to property and personnel in the immediate area.
The bouncing or vibration of the load caused by jogging may cause the lift straps, the load resting on the hook, or other load bearing lines to be momentarily disengaged from the load bearing portion of the hook, sometimes bouncing back out of the throat area of the hook, thereby causing complete disengagement of the load. In that regard, in the past various catch mechanisms or spring hooks have been developed for the purpose of requiring that a specific operation occur before release of the load from the hook such as to prevent accidental disengagement through the throat of the hook or to otherwise be sure that the load is not disengaged until the user manipulates the latching mechanism to disengage the load. Most existing load securing devices require direct manipulation of a hook mounted safety latch to release the load.
In crane lifting operations, to expedite matters and to prevent as little inconvenience or time delay as possible, it would be desirable to have radio-controlled release of one or more load securing straps or chains on a device for lifting single or multiple items, respectively. As an added safety feature, the straps or chains should not be releaseable as long as a load item is suspended from each strap or chain.